Mass Transfer Thermodynamics through a Gas–Liquid Interface

Abstract

Molecular level information about thermodynamic variations (enthalpy, entropy, and free energy) of a gas molecule as it crosses a gas–liquid interface is strongly lacking from an experimental perspective under equilibrium conditions. Herein, we perform in situ measurements of water interacting with the ionic liquid (IL) 1-butyl-3-methylimidazolium acetate, [C4mim]­[Ace], using ambient pressure X-ray photoelectron spectroscopy in order to assess the interfacial uptake of water quantitatively as a function of temperature, pressure, and water mole fraction (x w). The surface spectroscopy results are compared to existing bulk water absorption experiments, showing that the amount of water in the interfacial region is consistently greater than that in the bulk. The enthalpy and entropy of water sorption vary significantly between the gas–liquid interface and the bulk as a function of x w, with a crossover that occurs near x w = 0.6 where the water–IL mixture converts from being homogeneous (x w < 0.6) to nanostructured (x w > 0.6). Free energy results reveal that water at the gas–IL interface is thermodynamically more favorable than that in the bulk, consistent with the enhanced water concentration in the interfacial region. The results herein show that the efficacy for an ionic liquid to absorb a gas phase molecule is not merely a function of bulk solvation parameters but also is significantly influenced by the thermodynamics occurring across the gas–IL interface during the mass transfer process.

The Influence of Water Vapor on the Electrochemical Shift of an Ionic Liquid Measured by Ambient Pressure X‐ray Photoelectron Spectroscopy

“…An Ag/AgCl is used as a QRE in order to appropriately control the WE. Recently, our group has utilized APXPS to examine IL/gas interfaces in the presence of water vapor [63–66] . Herein these studies are extended by examining the IL 1‐butyl‐3‐methyimidazolium acetate, [C 4 mim][OAc], as a function of water vapor pressure and external bias.…”

Lab-based operando x-ray photoelectron spectroscopy for probing low-volatile liquids and their interfaces across a variety of electrosystems

“…Ambient pressure XPS systems are nowadays available as established and long-utilized synchrotron facilities, as well as lab-based instruments. 13,[19][20][21][22][23][24] Historical developments of the latter has recently been presented. 25 In the past decade, a different investigation route was pursued utilizing mostly lab-based instruments and using low-volatile liquids that usually have sufficient electrical conductivity, mainly, ionic liquids (ILs) and/or polymeric electrolytes.…”

X-ray Photoelectron Spectroscopy with Electrical Modulation Can Be Used to Probe Electrical Properties of Liquids and Their Interfaces at Different Stages

“…Operando XPS with the application of an external electrical voltage bias, in either the dc or ac form, during data acquisition can be very useful in the investigation of such devices because of its ability to provide electrical and chemical information about the sample, which has been extensively used by our group. − Extending it to the investigation of liquids has been relatively slow, mostly because of vacuum requirements, which has been successfully overcome by using multiple pumping stages and efficient electron optics. Hence, nowadays ambient pressure XPS systems are available at both synchrotron facilities and via laboratory-based instruments. − A parallel investigation route has been pursued by using liquids with negligible volatility and sufficient electrical conductivity, mainly, ionic liquids and polymer electrolytes, enabling researchers to probe electrochemical properties and/or reactions with chemical specificity, rendering a wealth of electrochemical information. − …”